The invention relates generally to power-driven modular plastic conveyor belts and, more particularly, to modular plastic conveyor belts hingedly interconnected row to row by two-part hinge pins.
Conventional modular conveyor belts and chains are constructed of modular links, or belt modules, arranged in rows. Spaced apart hinge eyes extending from each end of the modules include aligned openings. The hinge eyes along one end of a row of modules are interleaved with the hinge eyes of an adjacent row. A pivot rod, or hinge pin, journalled in the aligned openings of interleaved hinge eyes, connects adjacent rows together end to end to form an endless conveyor belt capable of articulating about a drive sprocket or drum.
Because they do not corrode and are easy to clean, modular plastic conveyor belts are often used instead of metal belts. Usually, the hinge pins in plastic belts are also made of plastic. The hinge pins are typically circular in cross section and reside in circular openings in the hinge eyes. Relative motion between the hinge pins and the walls of the hinge eyes as the belt articulates about sprockets tends to wear both the hinge pin and the hinge eye wall. In abrasive environments, such as in conveying potatoes and other agricultural produce, this wear is accelerated by the intrusion of dirt and grit into the hinges of the belt.
Metal hinge pins are sometimes used to increase the wear life of the pins. But that does not do away with the relative motion between pin and hinge eye wall, and belt module wear at the hinge is still a problem.
Non-circular hinge strips made of a flexible material have been proposed to resist wear. Hinge eyes forming slots with flared ends permit the confined hinge strip to flex a limited angle without frictionally rubbing with the hinge eyes as the belt articulates. Such an arrangement is effective in increasing wear life, but the flexible hinge strip is inherently weak in shear strength and unsuitable for carrying heavy loads.
Some power transmission chains constructed of metal components use a pair of pins in each joint between consecutive groups of links. At each joint, one pin is wedged into the openings of one group of links and another pin, in rocking engagement with the first pin, is wedged in the openings of the adjacent group of links. In this way, relative motion is confined to the rocking surfaces of the metal pins. But transmission chains and modular conveyor belts operate in different environments and serve different purposes. Power transmission chains often are used in well-lubricated environments, relatively free of abrasives, as in internal combustion engines and other machinery in which the use of gears is impractical. Modular conveyor belts, on the other hand, are frequently used in very abrasive, non-lubricated environments to move various products over long distances.
Thus, there is a need for a modular plastic conveyor belt that can resist wear at the hinge for a long operating life even in abrasive environments.
This need and others are satisfied by a modular plastic belt having features of the invention. The belt is formed of a series of rows of belt modules having a conveying surface. Each row includes one or more belt modules extending from a forward end to a rearward end in the direction of belt travel. A first set of hinge eyes is arranged along the forward end, and a second set of hinge eyes is arranged along the rearward end. Openings formed in the hinge eyes extend from a first end to a second end. The openings are narrower at the first end than at the second end. The rows are arranged end-to-end with the first set of hinge eyes of a row interleaved with the second set of hinge eyes of an adjacent row. The rows are hingedly connected together to form a conveyor belt by a plurality of hinge pins, each of which is divided lengthwise into two parts: a first hinge pin member and a second hinge pin member. The first hinge pin member is disposed in the first end of the openings in the first set of hinge eyes of a row and in the second end of the openings in the interleaved second set of hinge eyes of the adjacent row. The second hinge pin member is disposed in the second end of the openings in the first set of hinge eyes of the row and in the first end of the openings in the interleaved second set of hinge eyes of the adjacent row. In this way, the first hinge pin member is restrained in the narrow first end of the opening from rotational motion with respect to the first set of hinge eyes of the row, but is free to roll or rotate relative to the second hinge pin member and to the second set of hinge eyes in the adjacent row. With the elimination of the relative sliding or scrubbing motion between pin and hinge eye and the introduction of rolling motion between the first and second hinge pin members, wear life is increased, especially in abrasive conditions.
In preferred versions of the conveyor belt, the hinge pin members are of identical cross-section. This reduces the number of unique parts and makes for easier assembly and repair, when needed. In one version, the hinge pin is divided into identical hinge pin members, such as flat strips. In another version of the invention, the hinge pins are formed as a single piece with a frangible region between the first and second hinge pin members to allow the unitized hinge pin to be inserted easily into the hinge eye openings. Subsequent flexing of the belt at the hinge breaks the frangible region and separates the unitized hinge pin into the first and second hinge pin members.
Confronting faces on the first and second hinge pin members that bear against each other may be parabolic, hyperbolic, ellipsoidal, circular arcs, V-shaped, or a combination of flat and curved surfaces, for example. To prevent the confronting faces of the hinge pin members from wearing quickly, the hinge pins can be made of durable materials, such as polyurethanes, polyamides, polyvinylchlorides, fluorocarbons, and stainless steel.
In another version, the hinge pin is manufactured with a flexible bridge connected between the first and second hinge pin members to form a living hinge in the pin between the two hinge pin members. Such a pin can be made by co-injection molding or co-extrusion, for example.
In another version, the openings are formed with a slotted portion at the narrow first end to restrain the hinge pin member confined therein and a sector-shaped portion of the second end to allow the associated hinge pin member freedom to rotate relative to the restrained hinge pin member. The openings may be oriented with an axis of symmetry in the direction of belt travel or oblique to the direction of belt travel.
Thus, a conveyor belt embodying features of the invention eliminates relative rubbing contact between hinge pin and belt module, thereby making such a conveyor belt particularly long-lasting in abrasive environments.